The present invention relates to hydraulic apparatus in general and more particularly to a hydraulic control apparatus comprising a hydraulic master cylinder and a hydraulic slave cylinder for operating a mechanism remotely located from the master cylinder, the hydraulic control apparatus being prefilled with hydraulic fluid and pretested prior to shipment to a motor vehicle manufacturer, for example, for installation in a motor vehicle.
It is now known to prefill with hydraulic fluid a motor vehicle clutch control apparatus comprising a master cylinder, a reservoir of hydraulic fluid and a slave cylinder for operating the throw out bearing of a mechanical diaphragm spring clutch. Such prefilled hydraulic control apparatus are shown for example in U.S. Pat. Nos. 4,407,125; 4,599,860; 4,503,678 and 4,506,507, all assigned to the assignee of the present application.
As is well known, prefilling with hydraulic fluid and pretesting hydraulic apparatus for operating motor vehicle mechanisms such as mechanical clutches presents the many advantages, for the motor vehicle manufacturer, of receiving a fully assembled mechanism comprising all of the components filled with hydraulic fluid and pretested for proper operation ready to install on a motor vehicle on the assembly line without requiring that the components be installed, separately connected by way of a flexible conduit, and filled after installation with hydraulic fluid while being purged of any atmospheric air contained in the apparatus.
Fast, efficient, and accurate prefilling of the hydraulic apparatus is critical to the commercialization of such prefilled control apparatus. Various filling methods are disclosed in the above-identified patents assigned to applicant's assignee. Specifically, in U.S. Pat. No. 4,407,125, liquid is supplied through the open top of the reservoir until the liquid bleeds out of a bleed port in the slave cylinder whereupon the filling is terminated. In U.S. Pat. Nos. 4,506,507 and 4,503,678, a port is provided in a side wall of the reservoir, vacuum is applied to the system through the port in the reservoir to evacuate the system, liquid is introduced into the system through the port, and the port is thereafter sealed with a plug which serves to allow flow of hydraulic fluid out of the reservoir upon excess pressure but prevents reverse flow.
Whereas the filling methods disclosed in these patents have proven to be generally satisfactory, there continues to be a need to improve the apparatus and methodology of filling to provide more reliable filling, less expensive filling, and faster filling.